For safe operation of an aircraft, the weight of the aircraft must be determined prior to take-off. Airlines (also referred to as: FAA/Part 121 “Air Carriers”) have strict departure schedules, which are maintained to maximize aircraft utilization each day. Today's airline operations typically do not place fully loaded aircraft upon scales as a means to measure the aircraft weight, and the distribution of that weight, commonly referred to as the aircraft Center of Gravity (“CG”), prior to an aircraft's departure (“dispatch”) from an airport gate.
On any single day within the United States, airlines average 28,537 departures; where each of these air carriers must determine the weight and CG for each aircraft prior to departure. United States population has progressively become heavier over the years; thereby the individual weight of each passenger on these aircraft has become heavier. Airlines around the world operate on very strict time-schedules, where even a short departure delay occurring early in the day can have a ripple effect and create scheduling problems throughout the airline's remaining flight schedule. Aircraft load planning is a crucial part of keeping an airline operating on schedule. A scheduled aircraft departure will commence its load planning process up to one year prior to the actual flight. Airlines do not offer ticket sales for a flight more than twelve months prior to the flight. As each ticket for a scheduled flight is purchased, the average passenger and average checked bag weights are assigned for each ticketed passenger into a computer program, continually updating throughout the year the planned load for that flight. Aircraft have a Maximum Take-Off Weight “MTOW” limitation. Airline load planning procedures use weight assumptions as to the weight of passengers and baggage loaded onto the aircraft, provided by Aviation Regulatory Authorities, to stay below the aircraft MTOW limitation.
Aircraft weights are limited by Federal Aviation Administration “FAA” Regulation. The FAA is the Regulatory Authority which regulates the design, development, manufacture, modification and operation of all aircraft operated within the United States, and will be referenced along with the term “Regulatory Authority” to indicate both the FAA and/or any governmental organization (or designated entity) charged with the responsibility for either initial certification of aircraft or modifications to the certification of aircraft. Examples of Regulatory Authorities would include: European Aviation Safety Agency “EASA”, within most European countries; Transport Canada, Civil Aviation Directorate “TCCA”, in Canada; Agência Nacional de Aviação Civil “ANAC” in Brazil; or other such respective Regulatory Authority within other such respective countries.
FAA Regulations (provided in the Code of Federal Regulations) are the governmental regulations, which detail the requirements necessary for an aircraft to receive certification by the Regulatory Authority within the United States. These would be equivalent to such regulations within the Joint Aviation Regulations “JARs” which are used in many European countries.
Title 14 of the Code of Federal Regulations, Part 25 refers to regulations, which control the certification of Air Transport Category aircraft (“Part 25 aircraft”.) Part 25 aircraft include most of the commercial passenger aircraft in use today. For example, Part 25 aircraft include: Boeing model numbers 737, 747, 757, 767, 777; Airbus model numbers A300, A310, A320, A330, A340, etc. The FAA regulations allow for control mechanisms to assure Part 121 air carriers manage aircraft loading procedures to confirm at the completion of the loading process that the aircraft load distribution remains within the aircraft's certified forward and aft CG limits.
In particular:
Title 14—Code of Federal Regulations:
Part 121-695, subparagraph (d)
§ 121.695 Load Manifest: All Certificate Holders                The load manifest must contain the following information concerning the loading of the airplane at takeoff time:        (a) The weight of the aircraft, fuel and oil, cargo and baggage, passengers and crewmembers.        (b) The maximum allowable weight for that flight that must not exceed the least of the following weights:                    (1) Maximum allowable takeoff weight for the runway intended to be used (including corrections for altitude and gradient, and wind and temperature conditions existing at the takeoff time).            (2) Maximum takeoff weight considering anticipated fuel and oil consumption that allows compliance with applicable en route performance limitations.            (3) Maximum takeoff weight considering anticipated fuel and oil consumption that allows compliance with the maximum authorized design landing weight limitations on arrival at the destination airport.            (4) Maximum takeoff weight considering anticipated fuel and oil consumption that allows compliance with landing distance limitations on arrival at the destination and alternate airports.                        (c) The total weight computed under approved procedures.        (d) Evidence that the aircraft is loaded according to an approved schedule that insures that the center of gravity is within approved limits.        (e) Names of passengers, unless such information is maintained by other means by the certificate holder.        
If an airline is found to be operating a Regulated aircraft with weights in excess of the aircraft's certified weight limitations, that airline is subject to Federal penalties and fines. It is a violation of Federal Law to knowingly operate an aircraft, when the aircraft weight has exceeded any of the Original Equipment Manufacture's (“OEM's”) certified weight limitations.
All air carriers must have FAA approved procedures in place (“an approved schedule”), in which the air carrier will follow such procedures to insure each time an aircraft is loaded, the load will be distributed in a manner that the aircraft CG will remain within the forward and aft CG limitations. The FAA and the specific air carrier develop these procedures, which are often referred to as “loading laws” and when implemented define how the aircraft is loaded. An accurate determination of the total passenger weight portion of a flight could most readily be accomplished by having a scale located at the entrance to the aircraft door, by which all weight that enters the aircraft would be measured. Though this solution sounds simple, having the measured weight of the passengers and their carry-on items could cause substantial disruption in an airline's daily flight schedule. Such disruption would occur moments before the aircraft is scheduled to depart and when it is discovered that the aircraft measured weight does not match the aircraft's planned, or computed, weight. Even if the weight differential is only a few hundred pounds, the flight would be delayed until the discrepancy was resolved. Numerous aircraft delays could result with many dissatisfied passengers, which could be required to be removed from their planned flight.
The FAA has established guidelines through the issuance of an Advisory Circular AC No: 120-27E, dated Jun. 10, 2005, “Aircraft Weight And Balance Control” in which an airline is allowed to determine aircraft weight through the adoption of a “weight and balance control program” for aircraft operated under Title 14 of the Code of Federal Regulations (14CFR) part 91, subparts 121, 125 and 135. Part 121 deals with scheduled air carrier operations, including airlines such as American, Delta, United and Southwest.
The aircraft operator will use approved loading schedules to document compliance with the certificated aircraft weight limitations contained in the aircraft manufacturer's Aircraft Flight Manual (AFM), for the compiling and summing of the weights of various aircraft equipment, fuel and payload weights, along with the AC120-27E weight designations for passengers and baggage. These types of loading schedules are commonly referred to as the Load Build-Up Method (LBUM).
The aircraft LBUM weight determinations are “computed” with the use of guidance from AC120-27E, which define the approved methods to determine the aircraft weight using “weight assumptions” which are independent of any requirement to use scales to measure of the aircraft total weight at dispatch. The fully loaded weight of the aircraft is established through a process of compiling the weights of various payload items based upon FAA approved “designated” average weights, for the varying elements such as passengers, carry-on baggage, checked baggage, crew weight, cargo weight and the weight of fuel loaded; onto a previously measured empty aircraft weight.
On the actual day of a flight, typically two hours prior to the departure of that flight, the airline's automated load planning program will transfer this particular flight plan to the desktop computer display of one of the airline's Flight Dispatchers. It is the responsibility of the Flight Dispatcher to then monitor the planned load of this flight as passengers check-in and board the aircraft. The number of passengers and checked bags are input to the load-planning program. Typically this process goes without interruption and the aircraft will dispatch on schedule, as planned. As the aircraft's door closes and the load-plan is closed-out by the Flight Dispatcher, the aircraft weight associated with the “planned load” will always match the aircraft weight associated with the “departure load” as submitted to the FAA; because both are based on the same collection of weight assumptions used in determining the LBUM. Use of an alternate means to physically measure the total aircraft weight, just as the aircraft door closes, and the possibility of the measured aircraft weight not matching the calculated weight of the LBUM, would have the airline facing a potential departure delay to resolve any difference in the two separate but parallel aircraft weight determinations. This potential for delay in the flight departure on as many as 2,500 daily flights for a single airline, results in the various airlines not willing to take the risk of hundreds of flight delays each day. Many if not most airlines currently dispatch their aircraft under FAA approved LBUM procedures; a method which helps to keep the airlines running on schedule. This also creates an incentive for airlines to continue to use the FAA approved assumed weights, irregardless as to whether the assumed aircraft weight determinations are accurate.
Accurate determination of aircraft take-off weight is an important part of load planning in that it not only adds to the safety of each flight it also is an important consideration regarding the overall life limitation of the aircraft. The aircraft weight can be incorrect by as much as 2,000+ pounds and a “properly balanced” aircraft will still take-off, using an extra 100 feet of the available 10,000 feet of runway.
In addition, accurate determination of take-off weight is important in planning and executing the take-off of the aircraft. In planning the take-off of the aircraft, the pilots rely on the take-off weight of the aircraft to determine the required aircraft speed at take-off and the length of the runway needed to reach that speed. A heavier aircraft requires a higher speed to take-off, and a longer runway to reach that speed, than does a lighter aircraft of the same model. If the aircraft weight is incorrect, then the take-off determinations of speed and runway length will also be incorrect. If the physical runway is shorter than what is needed, the aircraft could crash on take-off.
Thus, the LBUM determined aircraft weight at take-off is subject to the accuracy of the data provided. It is desired to provide some verification of the aircraft weight.
An aircraft is typically supported by plural and in most cases three pressurized landing gear struts. The three landing gears are comprised of two identical Main Landing Gear (“MLG”) struts, which absorb landing loads and a single Nose Landing Gear (“NLG”) strut used to balance and steer the aircraft as the aircraft taxi on the ground. Designs of landing gear incorporate moving components, which absorb the impact force of landing. Moving components of an aircraft landing gear shock absorber are commonly vertical telescopic elements. The telescopic shock absorber of landing gear comprise internal fluids, both hydraulic fluid and compressed nitrogen gas, and function to absorb the vertical descent forces generated when the aircraft lands. While the weight of the aircraft is resting on the ground, the weight of the aircraft is “balanced” upon three pockets on compressed gas within the landing gear struts.
Measuring changes in the three landing gear strut internal pressures, will in turn identify the aircraft CG, and identify the distribution and subsequent re-distribution of aircraft loads.
In spite of numerous variations in prior art for aircraft On-Board Weight and Balance Systems (“OBWBS”), no U.S. airlines currently use OBWBSs in their daily operations, but instead all major airlines typically use the LBUM to determine aircraft weight and CG.
Though the FAA may continue to assume aircraft weight determinations, as computed within the guidance of AC120-27E, to have zero errors in the aircraft weight determination; a statistical evaluation and review of the FAA approved methods finds significant errors in the LBUM weights which remain un-recognized by the FAA.